The mind-river flows in two directions: one, towards evil through the path of the senses, and the other towards wellbeing through the path of discrimination. The flow towards evil and sin is stopped with the help of discrimination and renunciation and it is made to flow towards wellbeing and good with the help of practice. (Sage Vyasa)
Practice of concentration without renunciation is dangerous and mere renunciation without the practice of concentration of mind on the ideal may lead to dryness and purposelessness. Without renunciation, practice is blind; without practice, mere renunciation is lame. Renunciation shows the way while practice gives the energy to proceed toward the spiritual goal.
In the Gita, Sri Krishna has very succinctly stated its essence: Whenever and for whatever reason the restless mind wanders away, curbing it from that, it must be brought under the subjugation of the self.
By constant practice, habits are formed and character is nothing but a collection of good habits. As habits become strong and deep, they take the form of samskaras or subconscious impressions which govern the mind from deep within. The impressions created by the practice of control of thought-waves are called Nirodha-samskaras or impressions of control. These in turn act as further subconscious impulses to control the thought-waves. Thus a noble cycle of control-impressions-control, is formed in a serious yogi.
Source – excerpts from an article by Swami Brahmeshananda